Prof. R. Bunsen on Flame Reactions. 83 



reducing flame. It is especially available for reducing metals 

 when it is desired to collect them in the form of films. 



II. Method of Examination in the various parts of the 



Flame. 



A. Behaviour of the Elements at High Temperatures. 



This is one of the most important reactions which can be em- 

 ployed for the detection and separation of substances. The pos- 

 sibility of producing, with the flame of the lamp alone, a tempera- 

 ture as high as or higher than that of the blowpipe, depends upon 

 the fact that the radiating surface of the heated body be made as 

 small as possible. The arrangement for bringing the substances 

 into the flame must therefore be on a very small scale. The pla- 

 tinum wire upon which the substance is heated must scarcely 

 exceed the thickness of a horsehair, and one decimetre in length 

 of the wire must not weigh more than 0*034 grm. It is impos- 

 sible to obtain the results hereafter detailed if a thicker wire than 

 this is employed. Substances which act upon platinum, or which 

 will not adhere to the moistened surface of the metal, are held 

 in the flame upon a thin thread of asbestos, of which a hundred 

 may be obtained from one splinter of the mineral. These threads 

 must not exceed in thickness one-fourth of that of an ordinary 

 lucifer-match. Decrepitating substances are ground to the finest 

 powder on the porcelain lamp-plate with the elastic blade (a) of 

 the knife (fig. 4), and drawn up on to a moistened strip of one 

 square centimetre of filter-paper. If the paper is then burnt, 

 being held with the platinum forceps, or, better, between two 

 rings of fine platinum wire, the sample remains as a coherent 

 crust, which now may without difficulty be heated in the flame. 



If the substance requires to be heated in the flame for a long 

 period, the holder (fig. 5) is used. The arm (a) is fastened to 

 the carrier (A), so fixed on the stand by a spring (as seen at B) 

 that it can be moved both horizontally and vertically. The glass 

 tube (fig. 6) is held on this arm (a), and the fine platinum wire 

 fused on to the tube thus held in the flame. The splinters of 

 asbestos are stuck into the glass tube (b), which slips into the 

 holder, and may then be moved with the carrier (A). The car- 

 rier (B) carries a spring-clamp for holding test-tubes which have 

 to be heated for a considerable time in a particular part of the 

 flame. The little turntable (C) contains nine upright supports 

 to hold the w T ire tubes (fig. 6) employed in the experiments. 

 By means of these arrangements a particle of the substance 

 under examination is brought into the flame, and its behaviour 

 in the coldest and hottest parts of the flame is ascertained, the 

 substance being examined with a lens after each change of tem- 



G2 



